1. Field of the Invention
The present invention relates to the field of integrated circuits and more specifically to the protection of a semiconductor chip against shocks.
The present invention more specifically relates to surface-mounted semiconductor chips, that is, semiconductor chips having their connection pads supporting conductive protrusions intended to be directly placed against metal areas of a support such as a printed circuit board, this type of mounting being generally called a flip-chip mounting.
2. Discussion of the Related Art
In a flip-chip mounting, to reduce the bulk, bare chips having their surfaces only coated with a thin insulating layer such as a silicon oxide layer are used.
Packaged chips, which are then bulky, are also used.
FIG. 1A shows a surface-mounted chip 1 mounted on a printed circuit 3 via balls 5 attached, on the one hand, to contact pads of the chip and, on the other hand, to tracks of a printed circuit board. The chip is a bare chip which only comprises a thin layer of an insulator 7 on its front surface side (the side supporting the connection balls).
FIG. 1B is a view of the front surface of chip 1, in an example in which connection balls 5 are uniformly distributed in a matrix over the entire chip surface.
The present invention typically relates to substantially square or rectangular chips having dimensions ranging between 0.4 mm and 3 cm.
This type of mounting has been widely developed but experience has shown that it has a high risk of being defective. It has, in particular, been noted that the balls crack at their installation on the printed circuit or after mounting on the printed circuit when the device containing the printed circuit is submitted to shocks (for example, when the chip is mounted in a cell phone printed circuit and the user drops his phone on a hard surface). The ball cracking causes misconnections and an immediate failure of the circuit, or a progressive failure after some time of use.